Compressor



April 10, 1951 H. w. BURDETT ET AL COMPRESSOR 2 Sheets-Sheet 1 FiledNov. 2'7, 1946 'imwa SECTION IMPELLER INTERMEDIATE 5: CT'ION STATIONALONGROTOR An:

FRANK B. F'AEa E.

HAR BY INVENTOR RY w. BURDETT.

ATTORNEY April 10, 1951 H. w. BURDETT ET AL 21,543,465

COMPRESSOR Filed Nov. 27, 1946 2 Sheets-Sheet 2 ATTORNEY Patented Apr.10, 1951 COMPRESSOR Harry W. Burdett, Ridgewood, N. J and Frank B. Page,Manchester, Conn., assignors to Wright Aeronautical Corporation, acorporation of New York Application November 27, 1946, Serial No.712,582

V 4 Claims. 1

This invention relates to fluid compressors and is more particularlydirected to fluid compressors of the centrifugal type.

The conventiona1 centrifugal compressor comprises radially extendingfluid impeller blades each disposed in a plane including the axis of thecompressor. ihe outlet of a conventional centrifugal compressor isprovided with relatively fixed diffuser vanes for converting therotational velocity of the compressed fluid into pressure head. Anobject of this invention consists in curving the discharge end of thecentrifugal impeller blades so that the rotating blades themselves areeffective to eliminate the rotational velocity of the compressed fluid.For this purpose, the rotatable impeller blades are provided with acurved rearward portion at their discharge ends to retard the rotationalvelocity of the compressed fluid. In addition, the radially inner andouter walls of the compressor are substantially axial at the dischargeend of the impeller blades thereby converting the radial flow. of thecompressed fluid into axial flow.

Other objects of this invention will become apparent upon reading theannexed detailed description in connection with the drawing in which:

Figure 1 is a sectional view through a single stage compressor embodyingthe invention;

Figure 2 is a perspective view partly in section of a multi-stagecompressor;

Figure 3 is a diagrammatic view illustrating the relation between theaxial velocity of the entering air, the rotational velocity of theimpeller and the entrance end of the impeller blades; and

Figure 4 is a graph illustrating the helix angle of the impeller bladesat each station along the impeller.

Referring to the drawing, a rotor member ID is surrounded by a shroud l2radially spaced therefrom to provide an annular space or path l4therebetween for the fluid to be compressed. The annular space or fluidpath It has an entrance section extending approximately between thedashed lines It and 18 (Figure 1), an intermediate section extendingapproximately between the dashed lines I8 and 25 and a discharge sectionextending approximately between the dashed lines 20 and 22. Asillustrated, the entrance section IB, l8 and the discharge section 20,22 of the annular fluid path l4 are both coaxial with the impeller axis24 and extend substantially axially therealong, with the dischargesection having a substantially larger diameter. The intermediate section18, 2B of the annular fluid path l4 smoothly joins said entrance anddischarge sections. A plurality of circumferentially spaced ribbon-likevanes 26 extend across said annular space M from the entrance section tothe discharge section, each of said vanes being secured to the rotor H]for rotation therewith. Forv simplicity only one vane 2'6 has beenillustrated in the perspective view of Figure 2 while in Figure 1 aportion of only one vane 26 has been illustrated and the intersection ofthe root end of only a pair of vanes 26 with the rotor it has beenindicated by the lines 28.

The rotor member H] is rotatable counterclockwise when viewed from theleft of Figures 1 and 2 and air or other gas to be compressed" entersthe relatively small diameter entrance section of the annular fluid path[4. In this entrance section, the entrance edges of the anes 26 aredirected so that the fluid enters the compressor substantially withoutshock and the vanes are curved to gradually impart rotational velocityto the entering fluid.

The design of the entrance end of the vanes 26 is diagrammaticallyillustrated in Figure 3. In Figure 3, the line 24 indicates the axis ofrotation of the compressor, vector 30 indicates the 1 rotationalvelocity of a vane 26, vector 32 indicates the axial velocity of theentering air and vector 34 indicates the velocity of the entering airrelative to said vane 26. As illustrated, the entrance edge of a vane 26is made substantially tangent to the vector 34 and each vane 25gradually curves as indicated. Obviously, at a particular rotative speedof the impeller, the tangential velocity of each vane 25 will vary withthe radial distance from the compressor axis so that the direction ofthe entrance edge of each vane varies radially along its entrance edge.

The vanes 26 gradually straighten and flatten out so that, upon enteringthe intermediate section of the annular fluid path I4, the vanes 26 aresubstantially co-planar with the compressor axis 24. Accordingly, thefluid to be compressed enters the vanes 26 substantially without shockand the curvature of the vanes is such as to gradually impart rotationalvelocity to the fluid.

The intermediate section l8, 20 oi the annular fluid path I4 flaresoutwardly in a downstream direction so that the fluid is compressedoutwardly by the centrifugal forces acting thereon. The vanes 25 aresubstantially co-planar with the compressor axis throughout theintermediate section [8, 20 except, at the downstream end of thissection, the vanes 26 curve forwardly in the direction of impellerrotation as indicated at 36.

This forward curvature of the impeller vanes 26 increases the rotationalvelocity of the compressor fluid thereby increasing the centrifugalcompression without a corresponding increase in speed of the compressor.That is, in the region of the forwardly curved vane portions 36, in onerevolution of the impeller a particle of the compressed fluid rotatesmore than one revolution as it moves radially outwardly and axiallyalong the impeller.

Upon leaving the intermediate section [8, the compressed fluid entersthe axially extending discharge section 28, 22 of the annular fluid pathl4. In this discharge section, the vanes 25ers curved rearwardly-thatis, opposite to the direction of the compressor rotationas indicated at38. As a result of this rearward curvature of the impeller vanes 26, therotational velocity of the compressed fluid is gradually decreased as itflows to the discharge end of the compressor so that, at the dischargeend, the compressed fluid preferably only has an axial velocity. Theslowing down of the rotational velocity of the compressed fluid by theimpeller vane portions 38 results in the compressed fluid doing work onthe impeller vanes thereby helping to rotate the compressor rotor memberl0. Thus, the rearwardly curved vane portions 38 not only help tostraighten out the flow of the compressed fluid but, in so doing, energyis extracted from the fluid to help rotate the compressor. In thedischarge section of the fluid path M, the shroud l2 converts theradially outward velocity of the compressed fluid to axial flow.

The aforedescribed curvature of each vane 26 is graphically illustratedin Figure 4 in which the helix angle is the angle between a planeincluding the impeller axis and passing through a point on the line ofintersection of a vane with the impeller and a tangent to said line ofintersection at said point. The specific magnitude of said angle at eachstation along the impeller will depend on such factors as the rotationalvelocity of the impeller rotor, the physical characteristics of theparticular fluid to be compressed, the magnitude of the compressionratio desired, etc. Thus, the forwardly curved vane portions may startanywhere along the intermediate section 18, 28-e. g. this forwardcurvature may start at the beginning of the intermediate section '18, 2cin order to provide a more gradual forward curvature.

The compressor may be provided with asecond stage as as illustrated inthe perspective view of Figure 2. Since the compressed fluid, leavingthe first stage, has no rotative or radially outward velocity, it isfree to return to the smaller diameter of the entrance to the secondcompressor stage.

As illustrated, the shroud I2 is not attached to the vanes 26 forrotation therewith, but as is conventional practice it may be. Thus,centrifugal compressors are generally provided either with a fixedshroud over corresponding edges of the impeller blades or a shroud issecured to the impeller blades along these edges. The appendant claimsare intended to be broad enough to cover these conventional alternativeconstructions.

With the a-foredescribed construction, the forwardly curved impellervane portions 36 provide a relatively high centrifugal pressure with arelatively low speed of the compressor rotor 10. Also, deceleration ofthe rotational velocity of the compressor fluid by the impeller vaneportions 38 results in a low relative velocity of the compressor fluidand the flow straightening vane portions 38 as compared to the usualfixed type of flow straightening vanes. Also, the rotating flowstraightening vane portions 38 provide for smooth uninterruptedcontinuity of the compressor fluid flow path therethrough as contrastedwith the interrupted flow path provided by fixed type flow straighteningvanes.

While we have described our invention in detail in its present preferredembodiment, it will be obvious to those skilled in the art, afterunderstanding ourinvention, that various changes and modifications maybe made therein without departing from the spirit or scope thereof. Weaim in the appended claims to cover all such modifications.

We claim as our invention:

1-. A centrifugal compressor comprising a rotatable member; a shroudradially spaced from said rotatable member to provide an annular fluidflow space therebetween, said annular'space having a portion flaringradially outwardly in a downstream direction relative to fluid flowtherethrough and merging at its downstream end with a substantiallyaxially extending portion of said annular space; and a plurality ofribbon-like vanes secured to said rotatable member and projecting acrosssaid space toward said shroud to divide said space into a plurality offluid flow paths; each of said ribbon-like vanes being substantiallyco-planar with the axis of said rotatable member along the upstream endof the outwardly flaring portion of said annular space, and, along thedownstream end of said outwardly flaring portion, said vanes beingcurved about said axis in the direction of rotation of said rotatablemember, and, along the axially extending portion of said annular space,said vanes being curved about said axis in the opposite direction.

2. A centrifugal compressor comprising a rotatable member; a shroudradially spaced from said rotatable member to provide an annular fluidflow space therebetween; said annular space having a substantiallyaxially extending upstream end section, a substantially axiallyextending downstream end section of larger radius than said upstream endsection, and an intermediate section joining said end sections; and

a plurality of circumferentially-spaced similar ribbon-like vanessecured to said rotatable memher and projecting across said space towardsaid shroud to divide said space into a plurality of fluid flow paths;each of said vanes being curved about the axis of said rotatable memberin the axially-extending upstream end section of said annular space forgradually imparting rotational velocity to the entering fluid and, alongthe upstream end of the intermediate section of said annular space, saidvanes being substantially coplanar with the axis of said rotatablemember, and, along the downstream end of said intermediate section, saidvanes being curved about said axis in the direction of rotation of saidrotatable member, and, along the axially extending downstream endsection, said vanes being curved about said axis in a direction oppositeto the direction of rotation of said rotatable member.

3. A centrifugal compressor comprising a rotatable member, a shroudradially spaced from said rotatable member to provide an annular fluidflow space therebetween, said annular space having a portion flaringradially outwardly in a downstream direction relative to fluid flowtherethroughand merging at its downstream end with a substantiallyaxially extending portion of said annular space; and a plurality ofribbon-like vanes secured to said rotatable member and projecting acrosssaid annular space toward said shroud to divide said space into aplurality of fluid paths; each of said ribbon-like vanes along at leasta portion of the outwardly flaring portion of said annular space beingcurved about the axis of said rotatable member in the direction ofrotation of said rotatable member, and, along said axially extendingportion of said annular space, said vanes being curved about said axisin the opposite direction.

4. A centrifugal compressor comprising a rotatable member; a shroudradially spaced from said rotatable member to provide an annular fluidspace therebetween; said annular space having a substantially axiallyextending downstream end section of larger radius than said upstream endsection, and an intermediate section joining said endsections; and'aplurality of circumferentially-spaced similar ribbon-like vanes securedto said rotatable member and projecting across said space toward saidshroud to divide said space into a plurality of fluid paths; each ofsaid vanes being curved about the axis of said rotatable member in theaxially extending upstream end section of said annular space forgradually imparting rotational velocity to the entering fluid, and,along at least the downstream end of said intermediate section, saidvanes being curved about said axis in the direction of rotation of saidrotatable member, and, along the downstream axially extending endsection of said annular space, said vanes being curved about said axisin a direction opposite to the direction of rotation of said rotatablemember. 7

HARRY W. BURDETT. FRANK B. PAGE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,042,506 De Vallat Oct. 29, 19122,083,996 John June 15, 1937 2,236,706 Damonte Apr. 1, 1941 2,284,141Funk May 26, 1942 2,354,653 Allen Aug. 1, 1944 2,446,552 Redding Aug.10, 1948 FOREIGN PATENTS Number Country Date 489,318 Great Britain July25, 1938

